This proposal is to continue research into the mechanisms of anaphylactic reactions in man. The basic approach is immunologic but biochemical and pharmacologic studies will also be executed. The major tool is an in vitro model, the antigenically-induced IgE-mediated release of histamine from isolated human leukocytes. A basic tenet of the approach is that the in vitro anaphylactic reaction is an active multi- step response of a viable cell which is similar to other secretory processes. The control of this process by agents which affect the cyclic AMP system and the functional state of the microtubules provides the major line of investigation. We also plan to extend our studies to the release of other mediators, particularly SRS-A and ECF-A. We will explore the cell type from which these mediators are released as well as the control of the release process in a fashion similar to our studies with histamine release. We are continuing work on the allergens which cause clinical disease, concentrating on ragweed antigen Ra5 and enzymatic fragments of this small protein antigen. We also intend to pursue the purification of the allergens in Hymemoptera venoms, which are important for the diagnosis and treatment of patients sensitive to insect stings. We continue to study the interaction of the basophil with the IgE-antibodies which sensitize it: in this context we will attempt to ascertain the number of IgE molecules necessary to sensitize the basophil and to detect heterogeneity either in the Fc portion of IgE or in the receptor for IgE on the basophil membrane. It has been shown that this in vitro system reflects the clinical situation and it is anticipated that information derived from an understanding of the mechanism and pharmacologic control of mediator release will influence the current therapy of allergic disease as well as promote the development of new pharmacologic and immunologic modalities of therapy.